Within the field of wireless telecommunications systems there exists a system referred to as the personal handy phone system, otherwise known as PHS. Within the personal handy phone system, a user of a portable or personal station is able to communicate with a user of another telecommunication device by way of a cell station by way of a wireless communication channel. To enable portable stations and cell stations to communicate with each other within the personal handy phone system a radio interface is utilized.
The radio interface of the personal handy phone system utilizes a 1.9 gigahertz (GHz) carrier frequency to transmit information between cell stations and portable stations by way of the wireless communication channel. The antennas of the portable stations and the cell stations receive this carrier frequency signal and provide it to a radio chip. The radio chip amplifies the received carrier frequency signal and then down converts the amplified signal into a 10.8 megahertz (MHz) intermediate frequency signal. The 10.8 MHz intermediate frequency signal is then digitally down converted into a digital baseband signal which is provided to the upper layer of protocol within the particular device (e.g., cell station or portable station) that initially received the 10.8 MHz intermediate frequency signal. The manner in which the 10.8 MHz intermediate frequency signal is digitally down converted into a digital baseband signal conventionally is discussed below.
FIG. 1 illustrates a block diagram of the components that are conventionally used within the personal handy phone system to digitally down convert a 10.8 MHz intermediate frequency signal 120 into a digital baseband signal 130. The 10.8 MHz intermediate frequency signal 120 of the personal handy phone system contains communication information which could include voice/sound data or other types of communication data. Within a conventional digital down conversion circuit 100, a 10.8 MHz intermediate frequency signal 120 is received by hard limiter 102 which provides a threshold for the intermediate frequency signal 120. Sampler 104 receives the intermediate frequency signal from hard limiter 102 and samples it with a 19.2 MHz clock signal. The 19.2 MHz clock signal is a standard frequency used within baseband chips of the personal handy phone system because it is an integral multiple of the symbol frequency. The symbol frequency is 192 kilobits per second for a great majority of the baseband systems of the personal handy phone system. Down converter 106 receives the resulting intermediate frequency signal from sampler 104 and digitally down converts it by mixing it with a 9.6 MHz clock signal. Down converter 108 receives the resulting intermediate frequency signal from down converter 106. Down converter 108 further digitally down converts the intermediate frequency signal by multiplying it by a 1.2 MHz signal produced by local oscillator 110 resulting in a digital baseband signal 130. The resulting digital baseband signal 130 is a 384 kilobits per second signal which is then transferred to the upper layer of protocol within the particular device (e.g., portable station and cell station) that initially received the 10.8 MHz intermediate frequency signal 120.
The problem with the prior art digital down conversion of a 10.8 MHz intermediate frequency signal into a digital baseband signal within the personal handy phone system is that it requires two digital down conversion stages (e.g., down converters 106 and 108). As such, the two digital down conversion stages necessitate more internal circuitry within the portable stations and cell stations of the personal handy phone system increasing system complexity, time to manufacture and product cost. Therefore, it would be advantageous to provide a system within the personal handy phone system that enables a 10.8 MHz intermediate frequency to be digitally down converted into a digital baseband signal using one digital down conversion stage. Further, it would be advantageous to provide such a system that utilizes the personal handy phone system standard frequency of 19.2 MHz, which is an integral multiple of the symbol frequency of 192 kilobits per second. The present invention provides this advantage.